1. Field of the Invention
The present invention is directed to equipment for administering gaseous anesthetic to a patient by means of a ventilator having an anesthetic reservoir connected thereto.
2. Description of the Prior Art
Inhalation anesthesia equipment having a closed circulation system is described, for example, in European Patent Application 0 121 255. To reduce consumption of anesthetic, the exhaled gas is re-supplied to the inspiration line leading to the patient. This occurs via a carbon dioxide absorber. Used oxygen and anesthetic gas can be added via additional lines. A carbon dioxide analyzer and an oxygen analyzer are connected to the expiration line for monitoring.
A similar anesthesia-ventilation system is disclosed in German Patent 29 45 472. In this system, the exhalation gas is collected in a bellows and mixed with fresh anesthetic gas. During the next inspiration phase, the gas mixture is conducted from the bellows to the patient via a carbon dioxide absorber. Any excess of fresh antesthetic gas is discharged into the environment via a valve.
Another inhalation anesthesia system is described in German OS 29 42 623, which also has a closed circulation path wherein fresh anesthetic gas is continuously supplied. In contrast to German OS 29 45 472, the excess gas is collected in a gas evacuator. From this gas evacuator, the gas can be forwarded to a separator in which the anesthetic can be reclaimed. Polluting the environment with anesthetic gas is thus avoided by collecting the excess gas.
A pulmonary ventilator is described in U.S. Pat. No. 3,741,208 which can be used as an inhalation anesthesia system having closed circulation. The pulmonary ventilator described therein is suitable for use as the ventilator in the equipment disclosed and claimed in the present application. U.S. Pat. No. 3,741,208 also teaches returning the exhalation gas to the inspiration line via a compressor, given a closed system, after undesired gas components such as carbon dioxide have been filtered out, and consumed gas components, such as oxygen, have been added.
All of the above known closed circulation inhalation anesthesia devices have in common supplying anesthetic gas, i.e., a mixture of anesthetic and oxygen, to the patient via an inspiration line, and re-supplying the exhalation gas to the inspiration line via filters. Consumed gas may be replaced, and excess gas may be eliminated to the environment, or may be discharged into a recovery system in these known devices. The composition of the gas mixture in the inspiration line, however, is not reliably determined in any of these known systems. With the exception of the system described in European Application 0 121 255, all of the systems operate with an excess of fresh anesthetic gas. There is no monitoring of the consumption of anesthetic gas in these systems. The loss in volume during a breath is measured using a spirometer in the system described in European Application 0 121 255, and using this value the measured oxygen concentration of the anesthetic gas consumption is calculated therefrom, however, the composition of the gas in the inspiration line is not known, or is at least uncertain. In all of the above system, the carbon dioxide absorber is disposed in the inspiration line, or immediately therebefore. The function of this absorber is not monitored at all, so that uncleaned gas would be returned to the patient given a saturation, or given a malfunction in this absorber.